Animate Excavator digging
The Boolean Modifier will come in handy here. It's not a physically accurate solution, but you can certainly fake it for illustration purposes. 



Boolean can carve out geometry based on a reference object. So in this case, you can create a transparent object to point the modifier to, which will do the carving. Parent it to your solid object so they move in sync.

I've made a demo file with a basic animation. You can download it here.